A study of presence of accessory foramina transversaria in dry human cervical vertebrae of South Indian origin.
The unique feature seen in the cervical vertebrae is the presence of foramina transversaria in the transverse processes of all the cervical vertebrae. In all except the seventh cervical vertebra, the foramen transversarium (FT) normally transmits the vertebral artery and vein and a branch from cervicothoracic ganglion (vertebral nerve).  The foramina transversaria are known to exhibit variations in their shape, size, and in number. Sometimes, there may be multiple FT or they may be absent. Etiology of such variations may be related to variations in the course of vertebral artery or may be related to development.  An accessory transverse foramen (AFT) is present as a smaller foramen posterior to the FT.  As a result, distortion of the course of vertebral artery may occur. The above variations in FT can cause complaints such as headache, migraine attacks, and fainting. 
Knowledge of anatomical variations of cervical spine is vital for surgical procedures that involve the screw fixation. The risk of damage to vertebral artery during surgical procedures increases in cases of osseous and vascular variations of cervical spine.  The anatomical knowledge of variations of FT is important for the clinicians, neurologists, neurosurgeons, and radiologists. 
There are enough studies and case reports regarding variations in the origin and course of vertebral artery. Relatively, fewer studies are available on the morphology and incidence of the AFT, especially in Southern India. Hence, the present study was undertaken with the objective to find out the incidence of accessory foramina transversaria (AFT) in the cervical vertebrae of South Indian origin.
MATERIALS AND METHODS
Analytical and cross-sectional study was performed on 100 adult dry cervical vertebrae of unknown age and sex. The study was carried out in the Department of Anatomy, Amala Institute of Medical Sciences, Thrissur, Kerala, India. 100 dried human cervical vertebrae were selected for study after excluding damaged and pathologically abnormal vertebrae from the department of anatomy. Of 100 cervical vertebrae, 45 were atypical (C1, C2, and C7) and 55 were typical cervical vertebrae (C3, C4, C5, and C6). All the vertebrae were macroscopically examined for the presence of AFT. Vertebrae having AFT unilaterally or bilaterally were separated and photographed. The data were compiled and descriptive analysis was done using Microsoft Excel software.
As the study was observational and done on dry human bones, ethical clearance was not required.
Of examined 100 (including both typical and atypical) cervical vertebrae, 20 vertebrae have shown the presence of AFT. Of 20 vertebrae, 12 were having unilateral AFT [Figure 1] and eight were having bilateral AFT [Figure 2]. The percentage of AFT was shown in Table 1.
Of 100 cervical vertebrae, 55 were typical vertebrae (C3, C4, C5, and C6). The incidence of AFT in these vertebrae was shown in Table 2.
Of 100 cervical vertebrae, 45 were atypical vertebrae (C1, C2, and C7). The incidence of AFT in these vertebrae was shown in Table 3.
From the observations as per the above tables, it was inferred that the presence of AFT was more common in typical cervical vertebrae as compared to atypical vertebrae. Unilateral AFT was more commonly seen. In the present study, atypical cervical vertebrae, namely C1 and C2, have not shown AFT at all. C7 vertebrae showed only unilateral AFT.
Developmentally, vertebrae form from the sclerotome portions of the somites, which are derived from paraxial mesoderm. The transverse processes of cervical vertebrae are directed laterally and slightly forward. Each transverse process presents an opening called FT. The FT is bounded by anterior root and anterior tubercle, costotransverse bar, posterior tubercle, and posterior root in order. The costal element is represented by anterior root, anterior tubercle, costotransverse bar, posterior tubercle, and distal part of the posterior root. Proximal part of the posterior root represents the true transverse element. Developmentally, FT is formed by fusion vestigial costal element and true transverse process of the cervical vertebra. The vertebral vessels and nerve plexuses are caught between these two bony elements. Developmentally, vertebral arteries are formed from cervical intersegmental arteries which arise from the dorsolateral aspect of the dorsal aorta. These arteries link up with one another and form the longitudinal anastomotic channels, except the seventh cervical intersegmental artery. Remaining arteries regress and modified to form the vertebral artery.  When there is failure in controlled regression, it leads to variations in the vertebral artery origin and course. As the vertebral artery passes through FT, variations in vertebral artery might lead to variations in foramen. Hence, it can be interpreted that the variations in the course of the vertebral arteries will lead to variations in FT. 
AFT may be unilateral or bilateral, in the present study, we observed that the incidence of AFT in cervical vertebrae was 20%, of which unilateral AFT was 12% and bilateral AFT was 8%. In Table 4, the incidence of the AFT in the present study was compared with various other studies.
From Table 4, we can see that incidence of AFT varies from 1.5% to 27.33%. A study done by Das et al.,  on 132 vertebrae, it was observed double foramina transversaria unilaterally and bilaterally only in two cervical vertebrae, respectively. However, Taitz et al.  from their study observed doubling of FT in 34 cases of 480 cervical vertebrae amounting to 7%. In the same study, it was also reported triple foramina transversaria in one vertebra and absent foramen in four vertebrae.  In the present study, 20 vertebrae showed AFT of 100, and we did not observe more than one AFT. In the present study, we also observed that the incidence of AFT is more in typical cervical vertebrae as compared to atypical. Of 133 cervical vertebrae studied by Chaudhari et al.,  double foramina transversarium was observed in 22 vertebrae (23.15%), of which unilateral double foramen was found in 14 vertebrae (14.73%), and the bilateral was found in 8 vertebrae (8.42%). The above results were more in conformity with our study. Compared to other South Indian studies done by Murlimanju et al.,  Ambali MP et al.,  Sumalatha and Manasa,  and Katikireddi et al.,  the present study results were more in line with the North Indian studies such as Patra et al.  and Choudhari et al.  Knowledge of variations in the morphology of FT in cervical vertebrae is clinically important because the course of the vertebral artery may be distorted under such condition. Even the presence of extraforaminal in the transverse processes may indicate multiplication of the number of structures running through them. Hence, understanding of such anatomical variations is very much relevant for clinicians, surgeons, and radiologists.
The sample size was small, limited to 100 vertebrae.
The incidence of AFT in the present study was 20%. AFT was more common in typical cervical vertebrae as compared to atypical vertebrae. Unilateral AFT was more commonly seen than bilateral AFT. The first and second cervical vertebrae (atypical) have not shown AFT at all. Among the atypical vertebrae, only the seventh vertebra showed unilateral AFT. A thorough knowledge of these variations will be helpful to clinicians, radiologists, and neurosurgeons.
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Motagi Vishwanath Manjunath (1), Dharwadkar Kavitarati (2), Kottapurath Raghavan Sugathan (1)
(1) Department of Anatomy, Amala Medical College, Amala Nagar, Thrissur, Kerala, India, (2) Department of Biochemistry, Amala Medical College, Amala Nagar, Thrissur, Kerala, India
Correspondence to: Motagi Vishwanath Manjunath, E-mail: email@example.com
Received: August 21, 2018; Accepted: September 12, 2018
Caption: Figure 1: Unilateral accessory foramen transversarium
Caption: Figure 2: Bilateral accessory foramen transversarium
Table 1: Percentage of AFT in cervical vertebrae Total number of Number of Unilateral Bilateral cervical vertebrae vertebrae AFT AFT with AFT N = 100 20 (20%) 12 (12%) 8 (8%) AFT: Accessory foramen transversarium Table 2: Percentage of AFT in typical cervical vertebrae Total number of Number of Unilateral Bilateral typical cervical vertebrae AFT AFT vertebrae with AFT 55 16 (29.09%) 8 (14.54%) 8 (14.54%) AFT: Accessory foramen transversarium Table 3: Percentage of AFT in atypical cervical vertebrae Total number of atypical Number of Unilateral Bilateral cervical vertebrae N=45 vertebrae AFT AFT with AFT C1 0 0 0 C2 0 0 0 C7 4 4 (8.88%) 0 AFT: Accessory foramen transversarium Table 4: Comparison of incidence of AFT with other studies Authors Number of Incidence Unilateral Bilateral cervical of AFT (%) AFT (%) AFT (%) vertebrae Das et al.  132 1.5 -- -- Taitz et al.  480 7 -- -- Murlimanju et 363 1.60 1.40 0.30 al.  Shah et al.  210 16.19 9.52 6.67 Sharma et al.  200 8 3.50 4.50 Gujar et al.  150 27.33 18 9.33 Akhtar et al.  174 14.36 11.49 2.87 Ambali MP et 163 14.72 4.90 9.81 al.  Chaudhari et 133 23.15 14.73 8.42 al.  Mishra et al.  220 14.09 4.54 9.54 Patra et al.  150 22 10.67 11.33 Sumalatha and 148 11.48 5.40 6.08 Manasa  Katikireddi et 100 3 2 1 al.  Present study 2018 100 20 12 8 AFT: Accessory foramen transversarium
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|Title Annotation:||Research Article|
|Author:||Manjunath, Motagi Vishwanath; Kavitarati, Dharwadkar; Sugathan, Kottapurath Raghavan|
|Publication:||International Journal of Medical Science and Public Health|
|Date:||Nov 1, 2018|
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